Aircraft and other passenger transport vehicles typically have on-board lavatories with vacuum toilet systems. These systems typically include a waste-receiving toilet bowl connected to a main waste tank via a sewer pipe or main waste line. A discharge or flush valve is typically mounted on the sewer pipe to selectively allow fluid communication between the toilet bowl and the main waste tank. To power the toilet system, the waste reservoir is maintained under a pressure that is substantially lower than the pressure in the waste-receiving toilet bowl, which is typically under the near-atmospheric pressure of the aircraft's passenger cabin. Thus, when the discharge valve is opened, the pressure differential between the bowl and the reservoir causes the waste in the bowl to be drawn through the pipe into the waste reservoir.
These discharge valves typically have a cylindrical housing with an inner chamber sized to contain a disk-shaped plate with a hole therein. One side of the housing has an inlet that is generally aligned with an outlet that is located on the opposite side of the housing. The waste-receiving toilet bowl is connected to the inlet by one portion of a sewer pipe, and the main waste tank is connected to the outlet of the valve housing via another portion of the sewer pipe.
A drive mechanism selectively rotates the disk-shaped plate between an open position and a closed position. In the open position, the hole in the disk-shaped plate is aligned between the inlet and the outlet, which allows fluid communication for the flushing of the vacuum toilet. In the closed position, the hole in the plate is moved away from the inlet and outlet area, such that it blocks fluid communication between the inlet and the outlet, preventing fluid flow from the pressure differential between the bowl and the reservoir.
In vacuum waste systems, this differential pressure is what drives the collected mixed media (which can be human waste along with other waste items, such as paper products) from the toilet bowl into the accumulation point (which is typically the main waste tank). The discharge valve should provide an interface for such a vacuum system without venting the pressure differential completely. It should also allow for the controlled addition of material into the ambient-pressure environment, while providing a leak-free obstruction that can be moved or rotated in a controlled manner so as to allow for the passage of a mixed media bolus from the ambient-pressure environment (e.g., the toilet bowl) to the low pressure environment (e.g., the waste tank). The discharge valve is then returned to its closed position in order to prevent further movement of media and/or waste into the waste tank until the next flush is activated. One example of a valve for use with a vacuum toilet is shown and described by co-owned U.S. Pat. No. 6,325,356.
While many discharge or flush valves are available that achieve these tasks, a number of problems have arisen associated with their reliability due to the deleterious nature of human waste on mechanical devices. For example, due to the high degree of differential pressure being controlled by the flush valve, waste may be ingested into the interior of the valve housing during the flush process, which contributes to corrosion of internal components. Additionally, ingested waste may dry and harden, preventing the actuation of the flush valve and significantly reducing the reliability of the valve. It is thus desirable to provide improved flush valves that seek to prevent ingestion of waste into the interior of the valve, which can improve the reliability and lifespan of the valve.